ATM cell assembling/disassembling system

Abstract: Successive received asynchronous transfer mode (ATM) data cells are stored in a cell reception buffer (1). All address information included in said received ATM cells in an address table (2) are registered, and the same address information in the address table (2) are updated when there is idle time for a process of assembling packet data from the ATM cells or when there is no empty area in the address table (2). In a packet reception buffer (4) successive received packet data are stored. The packet data stored in said packet reception buffer (4) are disassembled into ATM data on the basis of address information retrieved from the address table (2).

Description: BACKGROUND OF THE INVENTION The present invention relates to an ATM (asynchronous transfer mode) cell assembling/disassembling system and, more particularly, to a system for managing and controlling an address table for studying transmission address information when assembling and disassembling ATM cells. In a CLAD (cell assembling/disassembling) unit for disassembling and reassembling VBR (variable bit rate) system data, for instance packets, received from a LAN (local area network) such as ETHERNET, into and from ATM cells, an address table for registering address information is provided. The address information included in the received ATM cells such as a transmission source address SA indicative of the transmission source, VPI (virtual path identifier) for identifying different virtual path links that are multiplexed in the same physical layer connection on an ATM layer and VCI (virtual channel identifier) for identifying different virtual channel links in the virtual path connection are registered. When disassembling the received packet data from the LAN to generate ATM cell, the address table is retrieved by using a destination address DA of the received packet data as a retrieval key, and the ATM cell is generated on the basis of the retrieved VPI and VCI. In this prior art address table management and control system, when registering the transmission source address SA, VPI and VCI included in the received ATM cell message in the address table, the address table is retrieved. If these data have not yet been registered, they are additionally registered in the address table. If they have been registered, the registered contents are updated. In such prior art address table management and control system for address studying, the address table is retrieved for each received message by using ATM cells, costing much retrieval time and causing a great load on the address studying. From EP-A-0 406 759 an ATM switching network is known including a table circuit and a table controller controlling this table circuit. A virtual channel setting part of the table controller registers the virtual channel corresponding to the communication request. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an ATM cell assembling/deassembling system, which permits efficient address study without need of great load on the study. This object is solved by the features of claim 1. Claim 4 shows a method of assembling/disassembling an ATM cell according to the invention. In the above system, the control means updates the same address information in the address table by sorting the address information and delete a plurality of entries having the same address value except one when there is idle time for a process of assembling packet data from the ATM cells or when there is no empty area in the address table. The address information includes a transmission source address SA indicative of a transmission source, VPI (virtual path identifier) for identifying different virtual path links that are multiplexed in the same physical layer connection on the ATM layer and VCI (virtual channel identifier) for identifying different virtual channel links in the virtual path connection included in the received ATM cells. Other objects and features will be clarified from the following description with reference to attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 shows a block diagram showing an embodiment of the present invention. Fig. 2 shows a flowchart for explaining the operation of the embodiment; and Fig. 3 shows an example of data registered in the address table 2 in Fig.1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a block diagram showing an embodiment of the present invention. Referring to the Fig. 1, a cell reception buffer 1 stores successive received ATM cells. Of these cells, address information such as VPI, VCI and the transmission source address SA, included in BOM (beginning of message) cell, a leading cell in each message, are registered in an address table 2. A packet generator 3 assembles the stored cells in the cell reception buffer 1 into packet data and transmits the data in the form of packets to the LAN. A packet reception buffer 4 stores successive packet data from the LAN and retrieves the VPI and VCI corresponding to the destination address DA of each packet from the address table 2. A cell generator 5 generates ATM cells using the packets read out from the packet reception buffer 4 and the VPI and VCI retrieved from the address table 2 and transmits the generated ATM cells to a bus in the system. Fig. 3 shows an example of data registered in the address table 2. A destination address DA field, VPI field and VCI field are registered as respective corresponding entries. In this registration, the transmission source address SA of the BOM cell in the ATM cell received in the cell reception buffer 1 is registered in the destination address DA in the address table 2. This is done so because the disassembling of the received packet data to the ATM cells in the cell generator 5 requires the VPI and VCI corresponding to the destination address DA of the received packet data, and the destination address DA is the transmission source address SA at the time of the registration. An address table controller 6 controls the registration, the retrieval and a sort operation of the address table 2. In the registration operation, all address information in the received ATM cell is registered in the address table 2. When there is no empty area in the address table 2, or when there is idle time for a process of assembling the received ATM cells to the packet data, a process of simplifying or making the same address information into single information is executed through sorting of the table. Fig. 2 is a flow chart showing the operation of the embodiment according to the present invention shown in Fig. 1. The received ATM cells are read out sequentially from the cell reception buffer 1 (step S1). Of these read-out cells, VPI, VCI and the transmission source address SA as address information provided in the BOM, are registered in the address table 2 (step S2). In the registration operation in the address table 2, all address information of the BOM cell is registered irrespective of whether there is any previous registration. This means that, unlike the prior art, no study is made for checking whether there is any registration, remarkably reducing the registration time. As shown in the step S2, the transmission source address SA of the cell is registered in the DA field of the address table 2, VPI; in the VPI field, and the VCI; in the VCI field. The information thus is registered progressively and additionally in the empty areas. The packet generator 3 assembles the received ATM cells into the packet data and transmits the packet data in the form of packets to the LAN. The received packets from the LAN are successively stored in the packet reception buffer 4. The packet data is successively read out from the packet reception buffer 4 and the retrieval of the address table 2 is executed with the destination address DA of each packet as retrieval key to read out VPI and VCI corresponding to the destination address DA from the table 2. The cell generator 5 generates ATM cells on the basis of the packets read out from the buffer 4 and VPI and VCI read out with retrieval from the address table 2. While the address information is successively stored in the address table 2 in the step S2, when the transmission source receives a plurality of the same cells, a plurality of the same address information pieces are registered in the address table 2 at this time since no check whether there is any registration is done. If there still is an empty area in the address table 2 (step S3) and also if the number of cells stored in the cell reception buffer 1 is more than a predetermined threshold value (step S4), the processes of the reading out from the cell reception buffer 1 (step S1) and the registration of address information in the address table 2 are continued. If the number of cells stored in the cell reception buffer 1 is less than the threshold value (step S4), there is an idle time for the packet data generation process. This idle time is utilized to effect rearrangement (or sorting) of data in the address table 2 with the DA field (step S5). As a result, there are a plurality of entries having the same address value, they are all deleted except one (step S6). If data has been written in all the areas of the address table 2 so that no more data can not be written (step S3), the registered data are made to be single data through the same process as the steps S3 through S6. The above process of the steps S3 through S6 is executed in the address table controller 6. In the above way, the address information is all registered in the address table without making any check as to whether there is any registration. Further, when there is no empty area in the address table or when there is idle time for the cell processing, the same address information is made to be single data through sorting of the table with the DA field. In this way, the above effects are obtainable. As described before, in the conventional system, in which the check is made whether the address information is registered after the retrieval of the address table for each reception of the ATM cell message. In contrast, in the operation of the above embodiment, all address information is registered and the sorting of the table and making data to single data is executed at a certain timing, reducing the load on the address study and permitting more efficient and faster address study.

Claims: An ATM cell assembling/disassembling system comprising a cell reception buffer (1) for storing successive received ATM (asynchronous transfer mode) data, packet generation means (3) for assembling packet data from the ATM cells stored in said cell reception buffer, an address table (2) for registering address information included in said received ATM cells, a packet reception buffer (4) for storing successive received packet data, cell generation means (5) for disassembling the packet data stored in said packet reception buffer into ATM data on the basis of address information retrieved from said address table (2), and control means for controlling the registration and the retrieval of said address table, characterized in that said control means (S1 - S5) is operative to register all address information of said received ATM cells in said address table (2) at the time of the registration and update the same address information in said address table (2) when there is idle time for a process of assembling packet data from said ATM cells or when there is not empty area in said address table (2). An ATM cell assembling/disassembling system as set forth in claim 1, wherein said control means updates the same address information in said address table (2) by sorting the address information and delete a plurality of entries having the same address value except one when there is idle time for a process of assembling packet data from said ATM cells or when there is no empty area in said address table. An ATM cell assembling/disassembling system as set forth in claim 1, wherein said address information are such as a transmission source address SA indicative of a transmission source, VPI (virtual path identifier) for identifying different virtual path links that are multiplexed in the same physical layer connection on the ATM layer and VCI (virtual channel identifier) for identifying different virtual channel links in the virtual path connection included in the received ATM cells. A method for assembling/disassembling an ATM cell comprising steps of: storing successive received asynchronous transfer mode (ATM) data cells in a cell reception buffer (S1), assembling packet data from the ATM cells stored in said cell reception buffer, characterized in that the method comprises the steps of: registering (S2) all address information included in said received ATM cells in an address table, and update the same address information in said address table when there is idle time for a process of assembling packet data from said ATM cells (S3) or when there is no empty area in said address table, storing in a packet reception buffer successive received packet data, and disassembling the packet data stored in said packet reception buffer into ATM data on the basis of address information retrieved from said address table.

Inventors: SUGITA MASAHIRO, SUGITA, MASAHIRO, SUGITA, MASAHIRO, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1994
Main classification: H04L12
IPC codes: H04L12, H04Q11, H04L29